Here's someone that probably none of you have ever heard of. His name is Stanley Jordan.
Here he is playing Stairway to Heaven in 2 digferent styles on 2 different guitars at the same time. Guy's unreal.
Still, when these type questions get asked, you have to take into context the pioneers. Guys who were doing things on their instruments that no one even thought to even try before, let alone do. The biggest giant in this area is Jimi. Almost everyone who came after him copied what he was doing or tried to expound upon it. That's how you know Jimi is the greatest. He invented things on the guitar that blew everyone away.
For what it's worth, when Jimi was asked if he was the greatest guitarist, he laughed and said, No. When asked who he considered to be the greatest, he said, Phil Keagy.
Off topic and for anyone wondering, and for the record, Buddy Rich is the greatest drummer ever.